40 national geographic • april 2018
and T’s—divided into roughly 20,000 genes. The
tweak that gives East Asians thicker hair is a sin-
gle base change in a single gene, from a T to a C.
Similarly, the mutation that’s most responsible
for giving Europeans lighter skin is a single tweak
in a gene known as SLC24A5, which consists of
roughly 20,000 base pairs. In one position, where
most sub-Saharan Africans have a G, Europeans
have an A. About a decade ago a pathologist and
geneticist named Keith Cheng, at Penn State
College of Medicine, discovered the mutation
by studying zebrafish that had been bred to have
lighter stripes. The fish, it turned out, possessed a
mutation in a pigment gene analogous to the one
that is mutated in Europeans.
Studying DNA extracted from ancient bones,
paleogeneticists have found that the G-to-A sub-
stitution was introduced into western Europe
relatively recently—about 8,000 years ago—by
people migrating from the Middle East, who also
brought a newfangled technology: farming. That
means the people already in Europe—hunter-
gatherers who created the spectacular cave paint-
ings at Lascaux, for example—probably were not
white but brown. The ancient DNA suggests that
many of those dark-skinned Europeans also had
blue eyes, a combination rarely seen today.
“ What the genetics shows is that mixture and
displacement have happened again and again
and that our pictures of past ‘racial structures’
are almost always wrong,” says David Reich, a
Harvard University paleogeneticist whose new
book on the subject is called Who We Are and
How We Got Here. There are no fixed traits asso-
ciated with specific geographic locations, Reich
says, because as often as isolation has created
differences among populations, migration and
mixing have blurred or erased them.
Across the world today, skin color is highly
variable. Much of the difference correlates with
latitude. Near the Equator lots of sunlight makes
dark skin a useful shield against ultraviolet
radiation; toward the poles, where the problem
is too little sun, paler skin promotes the produc-
tion of vitamin D. Several genes work together to
determine skin tone, and different groups may
possess any number of combinations of differ-
ent tweaks. Among Africans, some people, such
as the Mursi of Ethiopia, have skin that’s almost
ebony, while others, such as the Khoe-San, have
skin the color of copper. Many dark-skinned
East Africans, researchers were surprised to
learn, possess the light-skinned variant of
SLC24A5. (It seems to have been introduced to
Africa, just as it was to Europe, from the Middle
East.) East Asians, for their part, generally have
light skin but possess the dark-skinned version
of the gene. Cheng has been using zebrafish to
try to figure out why. “It’s not simple,” he says.
When people speak about race, usually they
seem to be referring to skin color and, at the
same time, to something more than skin color.
This is the legacy of people such as Morton, who
developed the “science” of race to suit his own
prejudices and got the actual science totally
wrong. Science today tells us that the visible dif-
ferences between peoples are accidents of histo-
ry. They reflect how our ancestors dealt with sun
exposure, and not much else.
“ We often have this idea that if I know your skin
color, I know X, Y, and Z about you,” says Heather
Norton, a molecular anthropologist at the Univer-
sity of Cincinnati who studies pigmentation. “So I
think it can be very powerful to explain to people
that all these changes we see, it’s just because I
haveanAinmygenomeandshehasaG.”
aBoUt an hoUr aWaY from Morton’s collec-
tion, at West Chester University, Anita Foeman
directs the DNA Discussion Project. On a bright
fall morning, she’s addressing the latest partici-
pants in the project—a dozen students of varying
hues, each peering at a laptop screen. A few weeks
earlier the students had filled out questionnaires
about their ancestry. What did they believe their
background to be? The students had then sub-
mitted saliva samples for genetic testing. Now,
via their computers, they are getting back their
results. Their faces register their reactions.
One young woman, whose family has lived in
India as far back as anyone can recall, is shocked
to discover some of her ancestry is Irish. Another
young woman, who has grown up believing one
of her grandparents was Native American, is dis-
appointed to learn this isn’t so. A third describes
herself as “confused.” “I was expecting a lot more
Middle Eastern,” she says.
Foeman, a professor of communications, is ac-
customed to such responses. She started the DNA
Discussion Project in 2006 because she was inter-
ested in stories, both the kind that families tell
and the kind that genes tell. From early on in the
project, it was clear these were often not the same.
A young man who identified as biracial was angry